Computing systems have made significant contributions toward the advancement of modern society and are utilized in a number of applications to achieve advantageous results. Numerous devices, such as desktop personal computers (PCs), laptop PCs, tablet PCs, netbooks, game consoles, smart phones, servers, and the like have facilitated increased productivity and reduced costs in communicating and analyzing data in most areas of entertainment, education, business, and science. One common aspect of computing systems is the memory subsystem that is used to store data. Computing systems may include one or more types of memory, such as volatile random-access memory, non-volatile flash memory, and the like.
An emerging non-volatile memory technology is Magnetoresistive Random Access Memory (MRAM). In MRAM devices, data can be stored in the magnetization orientation between ferromagnetic layers. Typically, if the ferromagnetic layers have the same magnetization polarization, the cell will exhibit a relatively low resistance value corresponding to a ‘1’ bit state; while if the magnetization polarization between the two ferromagnetic layers is antiparallel the memory cell will exhibit a relatively high resistance value corresponding to a ‘0’ bit state. Because the data is stored in the magnetic fields, MRAM devices are non-volatile memory devices. MRAM devices are characterized by densities similar to Dynamic Random-Access Memory (DRAM), power consumption similar to flash memory, and speed similar to Static Random-Access Memory (SRAM).
MRAM devices typically employ an array of Magnetic Tunnel Junctions (MTJs). The MTJs can include two ferromagnetic layers separate by a thin insulator layer. Electrons can tunnel from one ferromagnetic layer into the other. However, the orientation of the magnetization on the ferromagnetic layers affects the rate of electron tunneling such that the junction can be switched between a low resistance state and a high resistance state.
When testing MTJ devices, a magnet can be placed over a wafer to induce a magnetic field in the MTJ devices. The applied magnetic field can be used to test features of the MTJ device. For accurately testing the MTJ devices, it may be necessary to accurately control the magnetic field produced by the magnet. As MTJ devices continue to be scaled, there is a continuing need to control the magnetic field with greater accuracy. Similarly, there may be a continuing need to improve control of the magnetic field for such purposes and characterizing performance of the individual dies on a wafer, to perform failure mode analysis, yield analyses, and the like.